NTSB: Driver sped up moments before Oklahoma parade crash

TULSA, Okla. – Federal investigators say the woman accused of driving her car into spectators at Oklahoma State University's homecoming parade and killing four people sped up as she approached the parade route.

The National Transportation Safety Board said Thursday that co-workers who saw 26-year-old Adacia Chambers before the crash said she seemed distracted. The NTSB said her "emotional distress" was the probable cause of the crash on Oct. 24, 2015.

The report says Chambers' car accelerated from 54 mph to 59 mph in the five seconds before she struck a police motorcycle blocking the roadway. The NTSB says she applied the brakes after hitting the motorcycle, though the report doesn't say how fast she was driving when she hit the crowd.

Chambers has pleaded not guilty to four counts of second-degree murder.